1. Field of the Invention
The present invention relates to a fuel cell vehicle equipped with a fuel cell system that has a water supply device adapted to supply humidifying water to a fuel cell stack and, more particularly, to a technology for avoiding associated delivery conduits and component parts from damages resulting from the freezing of water at a temperature below the freezing point.
2. Description of the Related Art
As counter measure to count environmental issues in recent years, particularly air pollutions resulting from exhaust gas emissions of automobiles and global warming issues resulting from carbon dioxide emission, a fuel cell technology has been attracting public attention as counter measure that is able to achieve clean emission and high-energy efficiency. A fuel cell serves as an energy conversion system that supplies hydrogen or hydrogen rich gas, serving as fuel, and air to an electrolyte-electrocatalyst composite body to allow electrochemical reaction to occur for thereby converting chemical energy to electrical energy. Particularly, a solid polymer electrolyte fuel cell employing a solid polymer membrane is low in cost and easy to be formed in a compact structure while having a high energy density and is highly expected to be applied as a power supply for a moving object such as an automobile.
By the way, with the solid polymer electrolyte fuel cell, the solid polymer membrane functions as an ion conductive electrolyte as a result of water being saturated and, also, has a function to separate hydrogen and oxygen from one another. If water content in the solid polymer membrane is insufficient, ion resistance increases to cause hydrogen and oxygen to mix with one another, resulting in an inability of serving as the fuel cell to generate electric power. In the meanwhile, with the solid polymer electrolyte fuel cell, when hydrogen ions dissociated in a hydrogen electrode as a result of generating electric power pass through the electrolyte membrane accompanied with movement of water, and the hydrogen electrode is liable to be dried. Also, if steam contained in hydrogen or air that are supplied is low in content, the solid electrolyte membrane tends to be dried in areas in the vicinity of respective reaction gas inlets.
Because of such reasons, there has been a need for the solid electrolyte membrane of the solid polymer electrolyte fuel cell to be supplied with water to humidify the solid polymer electrolyte in a positive manner up to now and, to this end, some kind of humidifying means has been employed for humidifying the electrolyte per se or for humidifying hydrogen and air to be supplied.
With such humidifying means in the solid polymer electrolyte fuel cell described above, a need arises for counter measure to be undertaken for countering the freezing of humidifying water in consideration of use in cold climates. A probability occurs in humidifying water that would freeze and expand in associated delivery conduits and component parts at a temperature below the freezing point, resulting in a fear of causing damages in no small measure such as damages in the delivery conduits and the component parts. Therefore, for the purpose of avoiding such an issue, a proposal has heretofore been made to provide a technology of recycling humidifying water into a freezing tank (see first related art: Japanese Patent Provisional Publication No. 2000-257430 and second related art: Japanese Patent Provisional Publication No. 2002-158024).